The present disclosure relates to a sheet feeding mechanism for feeding a sheet and an image forming apparatus provided with the same.
An image forming apparatus represented by a copier, a printer, a facsimile machine or a complex machine provided with these functions generally includes a sheet feeding mechanism for picking up sheets one by one from a sheet stack composed of a plurality of sheets stacked one over another and conveying them to an image forming unit. The sheet feeding mechanism includes a feed roller which rotates while being held in contact with the upper surface of the sheet stack to feed a sheet, and a separating member such as a separation pad which is arranged to face the feed roller. The separation pad has a function of applying a frictional force to the sheets other than the uppermost one and suppressing the feed of unnecessary sheets when the feed roller is about to feed a plurality of sheets from the sheet stack. These feed roller and separation pad tend to be worn down due to contact with the sheets and need a higher frequency of maintenance than other parts.
In recent years, there is an increasing tendency for user-maintainable image forming apparatuses. On the other hand, after maintenance operation, a user may forget to mount a feed roller or a separation pad. If the image forming apparatus is started in such a state, problems such as no feed of sheets and the simultaneous feed of a plurality of sheets occur.
Accordingly, an image forming apparatus provided with a sensor capable of detecting the presence or absence of a feed roller has been proposed as a conventional technology. In this image forming apparatus, unless the feed roller is mounted at a predetermined position, a separation pad which is pressed against the feed roller during a normal operation moves upward and a projecting plate projecting laterally to the separation pad rotates a roller detection arm at that time. By separating a switch flag of a photosensor from the photosensor utilizing a rotational force of this roller detection arm, the presence or absence of the feed roller is detected.
However, the structure of the image forming apparatus as described above has a problem that one photosensor can detect only the presence or absence of the feed roller and cannot detect the presence or absence of the separation pad. That is, if the separation pad is not mounted, a switching operation of separating the switch flag from the photosensor utilizing a movement of the separation pad cannot be performed. Thus, the absence of the separation pad cannot be detected. Further, since the switching operation of the photosensor cannot be performed similarly also when both the feed roller and the separation pad are absent, the absence of both the feed roller and the separation pad cannot also be detected.
Thus, the above structure further requires a sensor exclusively used for the separation pad to detect the presence or absence of the separation pad. However, if the sensors for individually detecting the presence or absence of the feed roller and the separation pad are respectively provided, production cost increases and a large space is necessary to install a plurality of sensors.
The present disclosure was developed to solve the above problem and an object thereof is to provide a sheet feeding mechanism capable of detecting the presence or absence of a feed roller and a separation pad by one detector and an image forming apparatus provided with the same.